XHOST

NAME

xhost −
server access control program for X

SYNOPSIS

xhost
[[+−]name ...]

DESCRIPTION

The
xhost program is used to add and delete host names or
user names to the list allowed to make connections to the X
server. In the case of hosts, this provides a rudimentary
form of privacy control and security. It is only sufficient
for a workstation (single user) environment, although it
does limit the worst abuses. Environments which require more
sophisticated measures should implement the user-based
mechanism or use the hooks in the protocol for passing other
authentication data to the server.

OPTIONS

Xhost
accepts the following command line options described below.
For security, the options that affect access control may
only be run from the "controlling host". For
workstations, this is the same machine as the server. For X
terminals, it is the login host.

−help

Prints a usage message.

[+]name

The given name (the plus sign is optional) is
added to the list allowed to connect to the X server. The
name can be a host name or a user name.

−name

The given name is removed from the list of
allowed to connect to the server. The name can be a host
name or a user name. Existing connections are not broken,
but new connection attempts will be denied. Note that the
current machine is allowed to be removed; however, further
connections (including attempts to add it back) will not be
permitted. Resetting the server (thereby breaking all
connections) is the only way to allow local connections
again.

+

Access is granted to everyone, even if they aren’t
on the list (i.e., access control is turned off).

−

Access is restricted to only those on the list (i.e.,
access control is turned on).

nothing

If no command line arguments are given, a message
indicating whether or not access control is currently
enabled is printed, followed by the list of those allowed to
connect. This is the only option that may be used from
machines other than the controlling host.

NAMES

A complete name
has the syntax ‘‘family:name’’ where
the families are as follows:

inet Internet
host (IPv4)

inet6

Internet host (IPv6)

dnet

DECnet host

nis

Secure RPC network name

krb

Kerberos V5 principal

local

contains only one name, the empty string

si

Server Interpreted

The family is
case insensitive. The format of the name varies with the
family.

When Secure RPC
is being used, the network independent netname (e.g.,
"nis:unix.uid@domainname") can be
specified, or a local user can be specified with just the
username and a trailing at-sign (e.g.,
"nis:pat@").

For backward
compatibility with pre-R6 xhost, names that contain
an at-sign (@) are assumed to be in the nis family.
Otherwise they are assumed to be Internet addresses. If
compiled to support IPv6, then all IPv4 and IPv6 addresses
returned by getaddrinfo(3) are added to the access list in
the appropriate inet or inet6 family.

Server
interpreted addresses consist of a case-sensitive type tag
and a string representing a given value, separated by a
colon. For example, "si:hostname:almas" is a
server interpreted address of type hostname, with a
value of almas. For more information on the available
forms of server interpreted addresses, see the
Xsecurity(7) manual page.

The initial
access control list for display number n may be set
by the file /etc/Xn.hosts, where
n is the display number of the server. See
Xserver(1) for details.

DIAGNOSTICS

For each name
added to the access control list, a line of the form
"name being added to access control list"
is printed. For each name removed from the access control
list, a line of the form "name being removed
from access control list" is printed.

SEE ALSO

ENVIRONMENT

BUGS

You can’t
specify a display on the command line because
−display is a valid command line argument
(indicating that you want to remove the machine named
‘‘display’’ from the access
list).

The X server
stores network addresses, not host names, unless you use the
server-interpreted hostname type address. If somehow you
change a host’s network address while the server is
still running, and you are using a network-address based
form of authentication, xhost must be used to add the
new address and/or remove the old address.